1. Field of the Invention
This invention relates generally to perpendicular magnetic recording systems, and more particularly to a system with fast switching of the magnetization direction of the perpendicular write head.
2. Description of the Related Art
Perpendicular magnetic recording, wherein the recorded bits are stored in a perpendicular or out-of-plane orientation in the recording layer, allows for ultra-high recording densities in magnetic recording hard disk drives. The write head must be able to write data not only at high bit-density but also at high data-rates. The write speed is particularly important in enterprise disk drives. However, the switching time for the write pole of the write head to switch from one magnetization direction to the other is a limiting factor as the data rate is increased. At high data-rates, the available magnetic flux from the write head, as seen by the recording layer on the disk, is dominated by the low-frequency flux output of the write head. The reason for such loss of write flux includes a slow intrinsic time-constant of the magnetization reversal in the main pole of the write head. Also, lower data-rate systems still require additional overshoot of the write current from the disk drive's write driver circuitry to aid in the magnetization reversal. This additional overshoot requires additional power from the write driver circuitry.
Perpendicular magnetic recording systems with high-frequency assisted writing using a spin-torque oscillator have been proposed. In these proposed systems, the write head with perpendicular write pole generates the perpendicular write field to the magnetic recording layer and a spin-torque oscillator generates a high-frequency auxiliary field to the recording layer. The auxiliary field may have a frequency close to the resonance frequency of the magnetic grains in the recording layer to facilitate the switching of the magnetization of the grains. These types of systems that use a spin-torque oscillator to apply a high-frequency field to the recording layer to assist writing by the perpendicular write head are described in U.S. Pat. No. 6,785,092 B2; US 2008/0137224 A1; and by J. G. Zhu et al., “Microwave Assisted Magnetic Recording”, IEEE Transactions on Magnetics, Vol. 44, No. 1, January 2008, pp. 125-131. However, these systems do not increase the switching speed of the magnetization of the perpendicular write pole.
Pending application Ser. No. 12/419,278 filed Apr. 6, 2009 and assigned to the same assignee as this application discloses a perpendicular magnetic recording system with an auxiliary coil and auxiliary pole that injects magnetic flux into the write pole at an angle to the primary or perpendicular axis of the write pole. The additional flux from the auxiliary pole, which is injected non-parallel to the primary magnetization of the write pole, exerts a torque on the magnetization of the write pole, thereby facilitating magnetization reversal of the write pole.
Thus for both high data-rate and lower data-rate perpendicular magnetic recording, what is needed is a write head and system that reduces the magnetization reversal time of the write pole and overshoot for the write pole without the application of a high-frequency auxiliary field to the recording layer and without the need for an auxiliary coil.